A man accused in some of the freeway shootings that put Phoenix drivers on edge for weeks pleaded not guilty Thursday as his defense lawyers questioned the strength of the evidence against him.

Attorneys for Leslie Allen Merritt Jr., 21, who was arraigned on 15 felony counts, including aggravated assault and carrying out a drive-by shooting, said outside court that the investigation by state police does not place him at the shooting scenes.

"We're going to work diligently to make sure that we investigate this fully, and we believe in his innocence," said Ulises Ferragut, one of Merritt's two attorneys.

Ferragut and attorney Jason Lamm also cited investigators' evolving timeline of the shootings. They plan to do their own investigation, looking into another person possibly admitting responsibility for any of the 11 shootings, Lamm said. They didn't identify that person or provide details.

"It's very, very early in the game to get hard confirmation on that," Lamm said.

Department of Public Safety investigators used ballistics tests to tie Merritt to four of the 11 shootings that occurred on Phoenix-area freeways between Aug. 22 and Sept. 10.

Merritt, who lacked the beard he had when he was arrested Sept. 18 and with his head newly shaven, said nothing in court except his name and date of birth.

Each of the four shootings carries a possible sentence of 20 to 30 years, Maricopa County Attorney Bill Montgomery has said. But prosecutors cautioned it was too early to predict sentencing or the outcome of a trial, and Lamm said a prison term of more than 100 years "is a theoretical possibility only."

"There's no practical likelihood of it ever happening," Lamm told Phoenix news station KNXT-TV on Thursday.

Montgomery still called the arrest significant enough that the public can rest easier.

"It appears to be the person who initiated what was going on at that time," he said. "We haven't had any incidents since then."

Investigators continue to review information, and more charges are possible, Montgomery said. The investigation into the other shootings remains open.

Eight cars were hit with bullets, and three were struck with projectiles such as BBs or pellets, most while driving along Interstate 10, according to authorities. The only injury was to a 13-year-old girl whose ear got cut by glass on Aug. 29.

Merritt was arrested at a Wal-Mart in Glendale. His arrest brought relief to some after Gov. Doug Ducey announced it on Twitter. His tweet saying, "We got him!" drew criticism for seemingly implying that Merritt was guilty.

Montgomery said the governor's tweet was not an issue in Merritt's ability to get a fair trial.

"Unless there were 6 million followers of that Twitter account, I don't think you can fairly say everyone was aware of it or could be impacted by it," Montgomery said.

The tweet illustrated the high emotion surrounding the case, Lamm said.

"Nevertheless, we will handle this from an objective assessment of the facts and evidence as opposed to hunches and emotion," he said. "By the way, Doug Ducey will not be on my jury. So I feel better about that."